Bolometer

The bolometer is a photondetector with an extremely
large sensing range. It is sensitive to all electromagnetic
radiation up in to cosmic radiationwavelengths. The basic
bolometer consists of a photonabsorber, an extremely sensitive
thermoelectric sensor and often a cooling system. When a photon
hits the absorber, its temperature increases slightly. This is detected
by the temperature sensor. The bolometer is very sensitive, but it has a long recovery time, usualy several milliseconds since the
last photon hit. If the frequency of photon hits is lower than
the recovery time, you will get an accumulative measurement of the
energy of all the photons.

If the time between each hit is longer than the recovery time, the output will indicate the energy of the last photon. Since the energy is dependent on the frequency of the electromagnetic radiation (The higher the frequency the higher the energy), You can use a bolometer to measure the EM frequency of the photon. For example if a x-ray photon hits the bolometer the output variation
will be higher than if a IR photon hits it. This means that the bolometer
can be used in broadbandspectroscopy as long as the time between each
photon hit is longer than the recovery time.